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Biomaterials > Exam 2: Alginate > Flashcards

Exam 2: Alginate Flashcards

1
Q

exact time of working time is ______

A

hard to determine clinically

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2
Q

working time begins with the

___ and ends just __________ of the impression material develops

A

start of mixing, before elastic properties

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3
Q

definitions of the working time and setting time show that…(2)

A
  1. working time begins at start of mixing and ends just before elastic properties
  2. b/t working time and setting time the material continues to harden until no
    more changes in the mechanical properties occur.
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4
Q

high viscosity is a….

A

thick liquid

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5
Q

low viscosity is a…

A

thin liquid

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6
Q

viscosity is a ______

A

mechanical property

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7
Q

viscosity: a measure of its

resistance to ______ by ____ stress or ____ stress

A

gradual deformation, shear, tensile

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8
Q

viscosity depends on…

A
  • composition
  • rate of deformation (shearing)
  • temperature
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9
Q

the higher the molecular weight of a polymer, the _____ the viscosity

A

higher

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10
Q

the higher the filler content, which does not deform, the ____ the viscosity

A

higher

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11
Q

where a material is placed directly into the mouth, where it sets

A

direct restoration

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12
Q

examples of direct restorations

A

amalgam, resin composites

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13
Q

examples of indirect restorations

A

dentures, ceramics

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14
Q

where a restoration or prosthesis is prepared in a laboratory

A

indirect restoration

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15
Q

what does Combe’s law state?

A

restoration/appliance fabricated in the
lab cannot be more accurate than the
impression from which a working cast is
prepared

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16
Q

stages of impression taking

A
  1. insertion
  2. setting
  3. removal
  4. cooling to room temp
  5. disinfection
  6. storage
  7. compatibility with gypsum
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17
Q

alginate is…

A

an irreversible hydrocolloid

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18
Q

working time ___ with increase temperatures

A

decreases

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19
Q

when the impression material is removed from the mouth, it is in _______

A

an elastic state

20
Q

general requirements of impression material

A 
B = nontoxic/nonirritating
I = good wetting
C = long shelf life
M = good resistance to tearing
E = acceptable odor/taste
P = appropriate working/setting time
21
Q

notes on dimensional stability/accuracy

A
  • impressions are hydrophilic
  • working time/viscosity are important
  • once removed, enough elasticity for removal & enough strength to resist tearing
  • disinfection shouldn’t change impression
22
Q

two types of elastic materials

A

elastomers, hydrocolloids

23
Q

_____ materials are rigid when set, and will deform or fracture when displaced from undercuts

A

non-elastic

24
Q

_______ are aqueous materials, with poor strength and stability

A

hydrocolloids

25
Q

_______ are non-aqueous synthetic rubbers, which are more stable and stronger than hydrocolloids

A

elastomers

26
Q

hydrocolloid dispersion medium

A

water

27
Q 
a suspension of finely
divided particles (dispersed), suspended
uniformly in a dispersion medium
(dispersant) from
which the particles do not settle out
rapidly/cannot readily be
filtered
A

colloid

28
Q

can a colloid be readily filtered?

A

no

29
Q

a colloidal dispersion of very small

particles in a continuous liquid medium

A

sol

30
Q

a suspension where the dispersed phase

forms agglomerates in the form of chains or fibrils

A

gel

31
Q

sol is a ___ while gel is a _____

A

fluid; elastic solid

32
Q

loss of fluids by the material

A

syneresis

33
Q

uptake of fluids by the material

A

imbibition

34
Q

syneresis results in ____

A

shrinkage

35
Q

imbibition results in ____

A

expansion

36
Q

main components in alginate

A

water, powder

37
Q

what is the powder in alginate?

A
  • soluble salt of alginic acid
  • Ca salt
  • trisodium phosphate
  • filler
38
Q

what is the alginic acid in alginate?

A

sodium alginate

39
Q

sequential reactions of alginate

A
  • formation of calcium phosphate (1. retarder)

- formation of calcium alginate (gel) (2. setting)

40
Q

marks of good alginates

A
  • well defined working time
  • elastic
  • records fine detail
  • comparatively inexpensive
41
Q

marks of poor alginates

A
  • dimensionally unstable

- tears easily

42
Q

trisodium phosphate acts as a….

A

retarder

43
Q

purpose of calcium salt in alginate

A

provides reaction for sol to gel (setting mechanism)

44
Q

prevent tearing by removing impression with a…

A

sharp movement

45
Q

best use for study casts…

A

prosthodontics/orthodontic

46
Q

study casts are insufficient/unstable for…

A

bridges, inlays, crowns

Biomaterials (18 decks)

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